Removing degraded coatings and liners is the first step to reconditioning the inside surface of a pipe and is performed before new coatings or liners are applied. The inside surfaces of some larger pipes may be reconditioned while the pipes remain in the ground. Such may be the case for example for sewer pipes. In other cases, for example removing and replacing the insider liners of oil pipelines, sections of pipe are removed from the pipeline, collected and delivered to be reconditioned at a remote location.
High pressure water may be used to remove the inside liners of pipes by hydrodemolition, namely by fluid blasting the exposed surface to disintegrate and remove the liners. In the case of embedded or installed pipes, it is generally known to mount hydrodemolition nozzles on robots or to tow separate high pressure water nozzle assemblies along the inside of the pipeline by remote controlled tractors. The robot or the tractor moves along the inside of the pipe while the nozzles treat the inside surfaces. Examples of such systems are disclosed in U.S. Pat. No. 8,394,205 and WO 00/06312, both to MacNeil et al.
The use of in-pipe robots or tractors is inconvenient in the case of pipe sections that are short and small enough to be transported to a remote location to be treated. Robots and tractor systems require repeatedly reinstalling the robot or tractor assembly within successive relatively short pipe sections, in each case reattaching hoses and resetting the apparatus for the new pipe section to be worked. In oil pipeline reconditioning as in the case of many other types of pipes, reducing the turn-around time is of primary importance to the customer.
Treating the inside of a pipe using high pressure water nozzles also requires providing sufficient articulation and movement of the nozzles or nozzle assemblies to enable the water to work the entire circumferential area within the pipe. Various articulation arrangements have been proposed. One example is E.P. 1,565,279 to MacNeil et al. that discloses a wheeled frame that supports opposed pivotable and extendible arms, the distal ends of which comprise nozzle assemblies.
The use of various materials to line conduits such as pipelines and the like is well known and essential in many industries. For instance, in the field of piping crude or diluted bitumen from tar sands extraction to a storage facility or refinery, the internal surface of the metal pipe segments (each segment being typically 50 feet in length) that comprise the pipeline are often lined with a layer of a rubber compound (usually about 0.25 inches thick) that is adhered to the metal on the inside of the pipe, followed by a urethane layer (usually about 0.75 inches thick) that is adhered to the rubber layer. In other applications, the lining material may vary in thickness, composition or in other aspects. The lining of the pipelines wears or deteriorates over time, and it becomes necessary to periodically remove and replace the affected pipe segments in the pipeline. Being of different materials and thickness, each of the two layers requires a different set of operating conditions for its removal. A urethane layer having a thickness of about 0.75 inch may typically be removed by a single pass of water jets that are mounted within a few inches of the surface of the urethane and at a pressure of 15,000-20,000 psi. The number of nozzles may be varied so that a given area of surface is targeted by more than nozzle in succession thereby varying the operational parameters required to completely remove the urethane. The subsequent removal of an underlying rubber liner that is about 0.25 inch thick may be accomplished by a single pass using ultra-high water pressures of about 40,000 psi (using different nozzles). In fact, the individual layers may be removed variously using either high or ultra-high pressure water depending on operational parameters that include the distance of the nozzle from the surface, the number of passes by a nozzle, the debit volume from the nozzle, the spray pattern, movement or spinning of the nozzle and the dwell time. As a result, a first pass is typically conducted along the pipe section to remove the urethane layer using a first set of nozzles or operational parameters, followed by a second pass, using a second set of nozzles or operational parameters.
The use of high and ultra-high pressure water results in a significant amount of water and other debris (including shredded liner or pieces of liner), being displaced within the pipe, as well as introducing significant lateral stresses on the nozzle assemblies.
It is an object of this invention to provide a method and apparatus for treating the inside surface of pipe sections by hydrodemolition in an efficient manner.
It is a further object of this invention to provide a method and apparatus for efficiently removing the interior surface liners of pipe sections that have at least two layers of liner using hydrodemolition.
These and other objects of the invention will be better understood by reference to the detailed description of the preferred embodiment which follows. Note that the objects referred to above are statements of what motivated the invention rather than promises. Not all of the objects are necessarily met by all embodiments of the invention described below or by the invention defined by each of the claims.